GFS (Global Forecast System) Global Model from the "National Centers for Environmental Prediction" (NCEP)
4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC
Greenwich Mean Time:
12:00 UTC = 12:00 GMT
0.5° x 0.5° for forecast time <= 192 hrs
2.5° x 2.5° for forecast time > 192 hrs
Geopotential in 850 hPa (solid, black lines) and Temperature advection in K/6h (colored lines)
The map "T-Adv 850" shows the advection of cold or warm air at 850 hPa
level. Negative values indicate cold advection, while positive values
indicate warm air advection. Advection of warm or cold air causes the
geopotential height to respectively rise or drop, producing vertical rising
and sinking motion of air. There is, however, not a direct relationship
between temperature advection and resultant vertical motion in the
atmosphere since other lifting and sinking mechanisms can complicate the
picture, e.g. vorticity advection (see "V-Adv maps").
In weather forecasting, temperature advection maps are often used to locate
the postion of wam and cold fronts. Cold advection is common behind cold
fronts, while warm advection is common behind warm fronts and ahead of cold
fronts. Higher in the atmosphere temperature advection is getting less
pronounced, as horizontal much more uniform in temperature and the flow is
The Global Forecast System (GFS
) is a global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up to 16 days in advance, but with decreasing spatial and temporal resolution over time it is widely accepted that beyond 7 days the forecast is very general and not very accurate.
The model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour.
Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather. Although the first efforts to accomplish this were done in the 1920s, it wasn't until the advent of the computer and computer simulation that it was feasible to do in real-time. Manipulating the huge datasets and performing the complex calculations necessary to do this on a resolution fine enough to make the results useful requires the use of some of the most powerful supercomputers in the world. A number of forecast models, both global and regional in scale, are run to help create forecasts for nations worldwide. Use of model ensemble forecasts helps to define the forecast uncertainty and extend weather forecasting farther into the future than would otherwise be possible.
Wikipedia, Numerical weather prediction, http://en.wikipedia.org/wiki/Numerical_weather_prediction
(as of Feb. 9, 2010, 20:50 UTC).